Gold-Catalyzed Hydrohydrazidation of Terminal Alkynes

Article abstract of DOI:10.1021/acs.orglett.8b02019

Facile gold-catalyzed hydrohydrazidation of alkynes with various hydrazides R²CONHNH₂ (R = Alk or Ar; including those with an additional nucleophilic moiety) in the presence of Ph₃PAuNTf₂ (6 mol %) leading to a wide range of substituted keto-N-acylhydrazones (18 examples) in excellent to good yields (99-66%) is reported. This novel metal-catalyzed coupling proceeds under mild conditions (chlorobenzene, 60 °C), exhibits high functional group tolerance, and is insensitive to the electronic and steric effects of the substituents in the reactants.

Full text of DOI:10.1021/acs.orglett.8b02019

Letter
pubs.acs.org/OrgLett
Cite This: Org. Lett. XXXX, XXX, XXX−XXX
Gold-Catalyzed Hydrohydrazidation of Terminal Alkynes
Dmitry P. Zimin, Dmitry V. Dar’in, Valentin A. Rassadin,* and Vadim Yu. Kukushkin*
Institute of Chemistry, Saint Petersburg State University, Universitetskaya Nab. 7/9, 199034 Saint Petersburg, Russia
S
* Supporting Information
ABSTRACT: Facile gold-catalyzed hydrohydrazidation of alkynes with various hydrazides R2CONHNH2 (R = Alk or Ar;
including those with an additional nucleophilic moiety) in the presence of Ph3PAuNTf2 (6 mol %) leading to a wide range of
substituted keto-N-acylhydrazones (18 examples) in excellent to good yields (99−66%) is reported. This novel metal-catalyzed
coupling proceeds under mild conditions (chlorobenzene, 60 °C), exhibits high functional group tolerance, and is insensitive to
the electronic and steric effects of the substituents in the reactants.
old-catalyzed organic transformations stand among the
cutting-edge topics1,2,11,3−10 of modern chemistry, and in
Scheme 2. Different Routes of the Au-Catalyzed Reactions
of Alkynes
G
particular, these reactions are widely employed in the key steps
of total synthesis of natural products.12,13 Gold-based catalysis
is also used for the synthesis of varieties of heterocyclic
systems, which find numerous applications in medicinal
chemistry.14−25 The success of Au-catalyzed reactions is
typically based on high functional group tolerance and mild
reaction conditions.
Most common applications of the gold-involving catalysis
incorporate activation of unreactive alkynes toward nucleo-
philic addition (Scheme 1). It is generally believed that the
benzohydrazide reacted smoothly with phenylacetylene in the
presence of Ph3PAuNTf2 to yield the appropriate acylhy-
drazone, whereas pyridine N-oxides did not participate in the
observed transformation.
Scheme 1. Generation and Trapping of the Highly Reactive
Electrophilic AuI Species
To the best of our knowledge, such gold-catalyzed coupling
of N-nucleophiles and alkynes is hitherto unknown, and there
have been no reports concerning even similar reactions of
hydrazides. Only for the synthesis of gold−carbene complexes
have N-acylhydrazines been used.42 Our interest in the
gold(I)-catalyzed hydrohydrazination was further stimulated
by the available evidence that keto-N-acylhydrazones, formed
in the reaction, demonstrate antiviral (influenza A,43 HSV-144),
antitubercular,45,46 antiproliferative,47 anticonvulsant,48,49 and
antimicrobial50 activities, act as LSD-151 and G3BP252
inhibitors, and additionally are broadly employed in organic
synthesis.53−57 Herein, we report on a new high-yielding
approach toward acylhydrazones, which are generated under
mild conditions through nucleophilic addition of hydrazides to
alkynes in the presence of gold(I).
reaction of alkynes proceeds through an Au-activated alkyne
complex9 A before it is attacked by nucleophiles such as
water,26−28 alcohols,29−31 primary32−35 or secondary
amines,36,37 or hydrazines.38−40 The AuI-catalyzed reaction
with hydrazides relevant to this work has never been studied in
the past.
Previously, we have demonstrated that the multicomponent
reaction between alkynes, cyanamides, and pyridine N-oxides
in the presence of 5 mol % of Ph3PAuNTf2 is a synthetically
significant approach for the preparation of a series of
substituted 2-amino-1,3-oxazoles (Scheme 2).41 In an attempt
to expand the scope of the developed transformation, we have
surprisingly found that a simple replacement of cyanamide
with benzohydrazide dramatically changed the result. Thus,
Initially, this reaction was carried out in chloroform at 60 °C
employing 6 mol % of Ph3PAuNTf2 and an equimolar ratio of
phenylacetylene (1a) and benzohydrazide (2a). In the
attempted reaction, the target benzoylhydrazone (4aa) was
isolated in a moderate yield (66%; Table 1, entry 1). In order
Received: June 28, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.8b02019
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
to optimize the reaction conditions, we tested various solvents,
temperature, reagent ratios, amount of the catalyst, and
reaction time (Table 1).
59% when the reaction was conducted at 110 °C. The decrease
of the yield is probably because of a partial decomposition
and/or instability of the catalyst at 110 °C (Table 1, entry 7).
Regarding the reaction time, we observed that keeping the
reaction mixture at 60 °C for 2 h brings about an increase of
the isolated yield of 4aa up to 92% (Table 1, entry 8). Longer
heating as well as usage of a small excess of phenylacetylene
did not improve the yield (Table 1, entries 9 and 10). Finally,
we found that with a lower amount of Ph3PAuNTf2 (3 mol %)
the target hydrazone was isolated in 83% yield (Table 1, entry
11).
Table 1. Optimization of the Hydrohydrazidation
Conditions
a
conditions
To verify the scope and limitations of the developed
approach, several alkynes and hydrazides were tested (Scheme
3). In most cases, hydrazides 2 were obtained from easily
available carboxylic acid esters and hydrazine hydrate and
isolated in excellent yields. Commercially unavailable alkynes 1
were synthesized either from aryl halides through Sonogashira
coupling58 or from the appropriate aldehyde employing
Bestmann−Ohira reagent59 (for more details, see the
Supporting Information).
First, we tested several substituted benzohydrazides 1
bearing strong electron-donating (4-MeOC6H4) or strong
electron-withdrawing (4-NO2C6H4, 2-F3CC6H4) groups and
observed no or very small substitution effect on the reaction
time and yield of target N-acylhydrazones 4. Surprisingly
sterically hindered 2,4,6-trimethylbenzohydrazide (2e) reacted
smoothly with phenylacetylene (1a), and in this particular case,
the target product was isolated in good yield (82%).
Hydrazides obtained from aliphatic carboxylic acids such as
phenylacetic acid and cyclohexanecarboxylic acid gave target
products 4af and 4ag in 88 and 93% yields, respectively. To
demonstrate the potency of the developed approach, we
prepared heterocyclic hydrazides, viz. 3,4-dihydro-2H-benzo-
[b][1,4]dioxepine-7-carbohydrazide (2h) and furan-2-carbo-
hydrazide (2i) and employed these species in the studied
b
solvent
temp (°C)
time (h)
yield (%)
1
2
3
4
5
6
7
8
CHCl3
MeCN
DMF
EtOH
PhCl
PhCl
PhCl
PhCl
PhCl
PhCl
PhCl
60
60
60
60
60
90
110
60
60
60
60
1
1
1
1
1
1
1
2
3
2
2
66
66
c
traces
68
81
83
59
92
90
9
10
11
d
91
83
e
a
b
c
An equimolar ratio of 1a/2a was used. Isolated yield. Traces of the
product were detected in reaction mixture using ESI-MS. 1.2 equiv
d
e
of 1a was used. 3 mol % of Ph3PAuNTf2 was used.
First, we varied a few common solvents of different natures
(MeCN, DMF, EtOH, PhCl) and found that the application of
chlorobenzene led to the best synthetic results (Table 1,
entries 1−5). The effect of temperature and reaction time was
then studied. Increasing the temperature by 30 °C did not
significantly change the yield of benzoylhydrazone 4aa (Table
1, entry 6), whereas the isolated yield of 4aa dropped off to
Scheme 3. Reaction Scope with Various Terminal Alkynes and Hydrazides
B
DOI: 10.1021/acs.orglett.8b02019
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
system. These attempts were successful, and in both cases, the
corresponding products were isolated in 75 and 93% yields.
Second, we checked the behavior of terminal and internal
alkynes. In general, terminal alkynes were more reactive, and
the desired hydrazones 4 were formed in better yields than in
the case of internal triple bond species. Thus, derivatives of the
phenylacetylene bearing moderate electron-donating (4-
MeC6H4, 4-t-BuC6H4), strong electron-donating (4-
MeOC6H4), and electron-withdrawing groups (2-FC6H4, 4-
NCC6H4) as well as alkynes featuring bulky substituents next
to the reaction center (2,4,6-Me3C6H2) reacted smoothly, and
in all cases, acylhydrazones 4ba−ga were isolated in good
yields (71−81%). Expectedly, oct-1-yne reacted in the same
way as phenylacetylene. N′-(Octan-2-ylidene)benzohydrazide
(4ha) was obtained in 66% yield. All of our experiments
indicate that the Au-activated species9 can be easily generated
from terminal alkynes, and they exhibit high reactivity
independent of the substitution in the reactants.
Scheme 5. Reaction of Phenylacetylene (1a) with Bidentate
Nucleophiles 4j−k
When terminal alkynes were replaced by internal species 1i−
k, we observed a significant decrease of the reactivity and 4ia−
ka species were obtained in extremely low yields. However,
application of 12 mol % of Ph3PAuNTf2 allowed a slight
improvement of the yield of 4 (Scheme 4) Thus, for hex-3-yne,
(a molar ratio ca. 3:1) were formed in 99% overall yield. The
desired acylhydrazone 4ak was isolated as the major product
(58%), whereas the byproduct was formed after addition of the
second molecule of phenylacetylene (1a). For 2-mercapto-
benzohydrazide (2l), only traces of 2-mercapto-N′-(1-
phenylethylidene)benzohydrazide (4al) were detected in the
reaction mixture by HRESI-MS, most likely as a result of
possible deactivation of the gold(I) species by sulfur-
containing hydrazide under the reaction conditions; the high
affinity of gold(I) toward sulfur is well-known.
Scheme 4. Reaction of Internal Alkynes with
Benzohydrazide (2a)
In the context of the hydrohydrazidation, we were interested
in comparison of the reactivities of hydrazides and hydrazines.
Although these two classes of compounds are structurally
relevant, their reactivity in the studied transformation is not the
same. We found that the Ph3PAuNTf2-catalyzed coupling of
PhC(O)NHNH2 with PhCCH proceeds differently than the
attempted reaction with PhCH2NHNH2. It appears that the
hydrazine PhCH2NHNH2 does not react with phenylacetylene
under the optimized conditions because it reduces the
Ph3PAuNTf2 catalyst to colloid gold (detected after the
treatment).40,60−62 Furthermore, the reaction between PhCCH
(1a) and benzohydrazide (2a) is totally suppressed when the
equimolar amount of benzylhydrazine is added to the reaction
mixture, again because of the poisoning of the catalyst by its
reduction.
The contrasting reactivity of the hydrazides and hydrazines
could be rationalized upon consideration of the literature data.
Thus, a kinetic study indicated that RC(O)NHNH2 are 30−
70 times less nucleophilic than RNHNH2,63 and in addition,
more electron-deficient RC(O)NHNH2 species are weaker
reducing agents than the relevant hydrazines.64 Most likely, the
electron-accepting RC(O) group reduces nucleophilicity of
hydrazides and, concurrently, makes them substantially weaker
reducing agents than the relevant hydrazines, thus determining
the success of the studied gold-catalyzed reaction.
the corresponding N′-(hexan-3-ylidene)benzohydrazide (4ia)
was isolated in moderate yield (32%), whereas sterically
hindered 1,2-diphenylacetylene was unreactive, and target N′-
(1,2-diphenylethylidene)benzohydrazide (4ja) was isolated in
only intermediate yield and its application in the system gave a
mixture of regioisomers (a molar ratio 2:1) in total 37% yield.
All of these results indicate that the developed approach could
not be recommended as a synthetic procedure for the
preparation of acylhydrazones 4 from internal alkynes. In our
opinion, the problem of the low reactivity of internal alkynes
could be solved by using a more catalytically active gold
species, and this work is under way in our group.
The coupling proceeds unconventionally when benzohy-
drazides 2j−l bearing an additional nucleophilic moiety were
applied as the reaction partners (Scheme 5). Thus, 2-
hydroxybenzohydrazide (2j) reacted selectively, and we
observed only coupling of the alkyne and the NHNH2
functional group. The 2-hydroxy-N′-(1-phenylethylidene)-
benzohydrazide (4aj) was isolated in 99% yield.
To conclude, we developed a facile gold-catalyzed hydro-
hydrazidation based on an intermolecular reaction of the in
situ generated Au-activated terminal alkynes9 with various
hydrazides R2CONHNH2 (R2 = Alk or Ar) leading to keto-N-
acylhydrazones. In the case of phenylacetylene derivatives or
substituted benzohydrazides, the developed reaction proceeds
under mild conditions, exhibits high functional group
tolerance, and is insensitive to the electronic and steric effects
of the substituents in the aromatic ring, and in all studied
In the case of 2-aminobenzohydrazide (2k), the amino
group also took part in the transformation, and two products
C
DOI: 10.1021/acs.orglett.8b02019
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Letter
(22) Garzon, M.; Davies, P. W. Org. Lett. 2014, 16, 4850.
(23) Ueda, H.; Yamaguchi, M.; Kameya, H.; Sugimoto, K.;
Tokuyama, H. Org. Lett. 2014, 16, 4948.
instances, the target acylhydrazones were isolated in excellent
to good yields.
(24) Li, N.; Lian, X. L.; Li, Y. H.; Wang, T. Y.; Han, Z. Y.; Zhang, L.;
Gong, L. Z. Org. Lett. 2016, 18, 4178.
(25) Zeng, Z.; Jin, H.; Xie, J.; Tian, B.; Rudolph, M.; Rominger, F.;
Hashmi, A. S. K. Org. Lett. 2017, 19, 1020.
(26) Mizushima, E.; Sato, K.; Hayashi, T.; Tanaka, M. Angew. Chem.,
Int. Ed. 2002, 41, 4563.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.or-
glett.8b02019.
■
S
́
(27) Marion, N.; Ramon, R. S.; Nolan, S. P. J. Am. Chem. Soc. 2009,
131, 448.
Experimental procedures and analytical data of all
compounds; 1H, 13C{H} and HRMS (ESI) spectra
(PDF)
(28) Krauter, C. M.; Hashmi, A. S. K.; Pernpointner, M.
ChemCatChem 2010, 2, 1226.
(29) Teles, J. H.; Brode, S.; Chabanas, M. Angew. Chem., Int. Ed.
1998, 37, 1415.
(30) Santos, L. L.; Ruiz, V. R.; Sabater, M. J.; Corma, A. Tetrahedron
2008, 64, 7902.
AUTHOR INFORMATION
Corresponding Authors
■
*E-mail: v.rassadin@spbu.ru.
*E-mail: v.kukushkin@spbu.ru.
ORCID
́
́
(31) Leyva-Perez, A.; Rubio-Marques, P.; Al-Deyab, S. S.; Al-
Resayes, S. I.; Corma, A. ACS Catal. 2011, 1, 601.
(32) Mizushima, E.; Hayashi, T.; Tanaka, M. Org. Lett. 2003, 5,
3349.
Dmitry P. Zimin: 0000-0002-3191-8899
Vadim Yu. Kukushkin: 0000-0002-2253-085X
Notes
(33) Duan, H.; Sengupta, S.; Petersen, J. L.; Akhmedov, N. G.; Shi,
X. J. Am. Chem. Soc. 2009, 131, 12100.
(34) Yang, H.; Gabbaï, F. P. J. Am. Chem. Soc. 2015, 137, 13425.
̈
(35) Kramer, S.; Dooleweerdt, K.; Lindhardt, A. T.; Rottlander, M.;
Skrydstrup, T. Org. Lett. 2009, 11, 4208.
The authors declare no competing financial interest.
(36) Hesp, K. D.; Stradiotto, M. J. Am. Chem. Soc. 2010, 132, 18026.
(37) Skouta, R.; Li, C. J. Synlett 2007, 2007, 1759.
(38) Kinjo, R.; Donnadieu, B.; Bertrand, G. Angew. Chem., Int. Ed.
2011, 50, 5560.
(39) Morozov, O. S.; Gribanov, P. S.; Asachenko, A. F.;
Dorovatovskii, P. V.; Khrustalev, V. N.; Rybakov, V. B.; Nechaev,
M. S. Adv. Synth. Catal. 2016, 358, 1463.
(40) Manzano, R.; Wurm, T.; Rominger, F.; Hashmi, A. S. K. Chem.
- Eur. J. 2014, 20, 6844.
(41) Rassadin, V. A.; Boyarskiy, V. P.; Kukushkin, V. Y. Org. Lett.
2015, 17, 3502.
ACKNOWLEDGMENTS
■
V.A.R. gratefully acknowledges the support of the Scientific
Council of the President of the Russian Federation (Grant No.
MK-2382.2017.3). We are much obliged to the Center for
Magnetic Resonance and Center for Chemical Analysis and
Material Research (both belonging to Saint Petersburg State
University) for physicochemical measurements that were
conducted under Russian Foundation for Basic Research
project 18-33-00277. We thank a reviewer for the stimulating
idea of comparison of the reactivities of hydrazides and
hydrazines in the gold-catalyzed reaction with terminal alkynes.
̌
(42) Tsupova, S.; Rudolph, M.; Rominger, F.; Hashmi, A. S. K. Adv.
Synth. Catal. 2016, 358, 3999.
(43) Barman, S.; You, L.; Chen, R.; Codrea, V.; Kago, G.;
Edupuganti, R.; Robertus, J.; Krug, R. M.; Anslyn, E. V. Eur. J. Med.
Chem. 2014, 71, 81.
(44) Dawood, K. M.; Abdel-Gawad, H.; Mohamed, H. A.; Badria, F.
A. Med. Chem. Res. 2011, 20, 912.
(45) Sriram, D.; Yogeeswari, P.; Madhu, K. Bioorg. Med. Chem. Lett.
2005, 15, 4502.
(46) Bonnett, S. A.; Ollinger, J.; Chandrasekera, S.; Florio, S.;
O’Malley, T.; Files, M.; Jee, J. A.; Ahn, J.; Casey, A.; Ovechkina, Y.;
Roberts, D.; Korkegian, A.; Parish, T. ACS Infect. Dis. 2016, 2, 893.
REFERENCES
(1) Hashmi, A. S. K. Chem. Rev. 2007, 107, 3180.
(2) Corma, A.; Leyva-Perez, A.; Sabater, M. J. Chem. Rev. 2011, 111,
1657.
(3) Dorel, R.; Echavarren, A. M. Chem. Rev. 2015, 115, 9028.
(4) Zheng, Z.; Wang, Z.; Wang, Y.; Zhang, L. Chem. Soc. Rev. 2016,
45, 4448.
■
́
́
(5) Miro, J.; Del Pozo, C. Chem. Rev. 2016, 116, 11924.
(6) Li, Y.; Li, W.; Zhang, J. Chem. - Eur. J. 2017, 23, 467.
̌
́
̌
́
́
́
́
̊
(47) Hruskova, K.; Potuckova, E.; Hergeselova, T.; Liptakova, L.;
(7) Furstner, A. Angew. Chem., Int. Ed. 2018, 57, 4215.
̈
̌
̌
́
̌
́
̊
́
́
Haskova, P.; Mingas, P.; Kovaríkova, P.; Simunek, T.; Vavrova, K. Eur.
J. Med. Chem. 2016, 120, 97.
(8) Hashmi, A. S. K.; Rudolph, M. Chem. Soc. Rev. 2008, 37, 1766.
(9) Hashmi, A. S. K. Angew. Chem., Int. Ed. 2010, 49, 5232.
(10) Braun, I.; Asiri, A. M.; Hashmi, A. S. K. ACS Catal. 2013, 3,
1902.
(48) Kulandasamy, R.; Adhikari, A. V.; Stables, J. P. Eur. J. Med.
Chem. 2009, 44, 4376.
(49) Kulandasamy, R.; Adhikari, A. V.; Stables, J. P. Eur. J. Med.
Chem. 2009, 44, 3672.
(11) Hashmi, A. S. K. Acc. Chem. Res. 2014, 47, 864.
(12) Rudolph, M.; Hashmi, A. S. K. Chem. Soc. Rev. 2012, 41, 2448.
́
(50) Ferreira, I. P.; Pilo, E. D. L.; Recio-Despaigne, A. A.; Da Silva, J.
̈
(13) Pflasterer, D.; Hashmi, A. S. K. Chem. Soc. Rev. 2016, 45, 1331.
G.; Ramos, J. P.; Marques, L. B.; Prazeres, P. H. D. M.; Takahashi, J.
A.; Souza-Fagundes, E. M.; Rocha, W.; Beraldo, H. Bioorg. Med. Chem.
2016, 24, 2988.
(14) Couty, S.; Meyer, C.; Cossy, J. Angew. Chem., Int. Ed. 2006, 45,
6726.
(15) Miege, F.; Meyer, C.; Cossy, J. Org. Lett. 2010, 12, 4144.
(16) Xu, W.; Wang, G.; Sun, N.; Liu, Y. Org. Lett. 2017, 19, 3307.
(17) Zeng, Z.; Jin, H.; Song, X.; Wang, Q.; Rudolph, M.; Rominger,
F.; Hashmi, A. S. K. Chem. Commun. 2017, 53, 4304.
(18) He, W.; Li, C.; Zhang, L. J. Am. Chem. Soc. 2011, 133, 8482.
(19) Xiao, Y.; Zhang, L. Org. Lett. 2012, 14, 4662.
(20) Gronnier, C.; Boissonnat, G.; Gagosz, F. Org. Lett. 2013, 15,
4234.
(51) Xi, J.; Xu, S.; Wu, L.; Ma, T.; Liu, R.; Liu, Y. C.; Deng, D.; Gu,
Y.; Zhou, J.; Lan, F.; Zha, X. Bioorg. Chem. 2017, 72, 182.
(52) Gupta, N.; Badeaux, M.; Liu, Y.; Naxerova, K.; Sgroi, D.; Munn,
L. L.; Jain, R. K.; Garkavtsev, I. Proc. Natl. Acad. Sci. U. S. A. 2017,
114, 1033.
(53) Yang, X. L.; Peng, X. X.; Chen, F.; Han, B. Org. Lett. 2016, 18,
2070.
(54) Ogawa, C.; Sugiura, M.; Kobayashi, S. J. Org. Chem. 2002, 67,
5359.
(21) Gronnier, C.; Bel, P. F. d.; Henrion, G.; Kramer, S.; Gagosz, F.
Org. Lett. 2014, 16, 2092.
D
DOI: 10.1021/acs.orglett.8b02019
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
(55) Xu, H.; Yang, P.; Chuanprasit, P.; Hirao, H.; Zhou, J. Angew.
Chem., Int. Ed. 2015, 54, 5112.
(56) Zhu, T.-H.; Wei, T.-Q.; Wang, S.-Y.; Ji, S.-J. Org. Chem. Front.
2015, 2, 259.
(57) Wang, Z.; Zhu, F.; Li, Y.; Wu, X. F. ChemCatChem 2017, 9, 94.
(58) Yamaguchi, Y.; Ochi, T.; Miyamura, S.; Tanaka, T.; Kobayashi,
S.; Wakamiya, T.; Matsubara, Y.; Yoshida, Z. I. J. Am. Chem. Soc.
2006, 128, 4504.
̈
(59) Bucher, J.; Stoßer, T.; Rudolph, M.; Rominger, F.; Hashmi, A.
S. K. Angew. Chem., Int. Ed. 2015, 54, 1666.
(60) Tatarchuk, V. V.; Sergievskaya, A. P.; Druzhinina, I. A.;
Zaikovsky, V. I. J. Nanopart. Res. 2011, 13, 4997.
(61) Ali, N.; Park, S. Y. Langmuir 2008, 24, 9279.
(62) Leong, W. L.; Lee, P. S.; Lohani, A.; Lam, Y. M.; Chen, T.;
Zhang, S.; Dodabalapur, A.; Mhaisalkar, S. G. Adv. Mater. 2008, 20,
2325.
(63) Nigst, T. A.; Antipova, A.; Mayr, H. J. Org. Chem. 2012, 77,
8142.
(64) Shacham-Diamand, Y.; Inberg, A.; Sverdlov, Y.; Bogush, V.;
Croitoru, N.; Moscovich, H.; Freeman, A. Electrochim. Acta 2003, 48,
2987.
E
DOI: 10.1021/acs.orglett.8b02019
Org. Lett. XXXX, XXX, XXX−XXX